<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
    <!-- 准备好一个容器 -->
    <div id="root">
       <h2>今天天气很{{info}}</h2>
       <button @click="changeWeather">切换天气</button>
       <hr/>
       <h3>a的值是: {{numbers.a}}</h3>
       <button @click="numbers.a++">点我让a+1</button>
       <h3>b的值是: {{numbers.b}}</h3>
       <button @click="numbers.b++">点我让b+1</button>
       <button @click="numbers = {a:666, b:888}">彻底替换掉numbers</button>
    </div>
</body>
<script type="text/javascript">
    Vue.config.productionTip = false //阻止 vue 在启动时生成产生提示
    const vm = new Vue({
        el: '#root',
        data: {
            isHot: true,
            numbers: {
                a: 1,
                b: 1
            }
        },
        computed: {
            info(){
                return this.isHot ? '炎热' : '凉爽'
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        watch: {
            isHot: {
                // immediate: false, //初始化时让 handler 调用一下
                //handler什么时候调用？ 当isHot发生改变时。
                handler(newValue, oldValue){
                    console.log('isHot被修改了', newValue, oldValue);
                }
            },
            //监视多级结构中某个属性的变化
            // 'numbers.a':{
            //     handler(){
            //         console.log('a被改变了');
            //     }
            // }

            //监视多级结构中所有属性的变化
            numbers: {
                deep: true,
                handler(){
                    console.log('numbers改变了');
                }
            }
        }
    })
    
</script>
</html>